This invention relates to a method for inactivating mycotoxins which may be present as contaminants in dry animal feeds by adding a selected type of montmorillonite clay. More specifically, the selected clay is a calcium montmorillonite clay in which the ratio of surface acidity (as determined by Hammett indicators in the 5.0-6.8 pKa range) to pore volume (in the 50-600 Angstrom range) is above 5 and is preferably above 10.
Mycotoxins, chemical substances produced by ubiquitous fungi, can make the difference between profit and loss to the poultry and livestock industries. Animals are extremely vulnerable to mycotoxins due to the common practice of diversion of mycotoxin contaminated agricultural commodities to animal feed. Thus, mycotoxicoses, or mycotoxin-induced diseases, frequently occur in animals.
It is readily apparent from a review of scientific literature that the most studied and prevalent of these agents are the aflatoxins, a group of closely related polysubstituted coumarin derivatives, which are biosynthesized by flavis and parasiticus species of Ascergillus fungi. The aflatoxins have invoked much concern as toxic food and feedborne agents following the discovery that they: 1) are potent carcinogens and mutagens, 2) are stable in foods and feeds and are relatively unaffected by a variety of processing procedures, 3) can be found as residues in the tissues of animals and humans, and 4) are associated with animal and human disease.
A preponderance of poultry and livestock exposure to aflatoxins is chronic in nature and occurs through the ingestion of low levels of these chemicals such as "marginally contaminated" rations which do not increase the mortality rate nor result in obvious signs of disease. Instead, chronic exposure to aflatoxins results in economically important effects in animals such as depression of growth rates, feed conversion and alteration of immunocompetency which can result in increased susceptibility to infection and decreased ability to resist stress.
Numerous approaches to reduction of aflatoxin levels in agricultural commodities have been experimentally assessed. These include mixing and dilution with aflatoxin-free grains in order to obtain a level within regulatory guidelines; physical methods of separation such as cleaning, density segregation and preferential fragmentation; solvent extraction; biological inactivation; thermal inactivation; and chemical inactivation with a variety of acids, aldehydes, oxidizing agents and alkalis. These approaches have been relatively unsuccessful on a commercial scale due to lack of efficacy, economic constraints of the protocol, unacceptable alteration of feed quality, or the introduction of potentially deleterious substances. Consequently, simple, cost effective, practical and safe processes by which animal feeds can be decontaminated or detoxified are in great demand.
Clays such as montmorillonite have previously been incorporated into poultry feed at levels as low as one percent of the animal ration as in U.S. Pat. No. 3,687,680. Effects accompanying the addition of montmorillonite included increased growth rate and body weight of the chickens and reduced mortality rate. Dietary additions of zeolites (Smith, J. Animal Science. 1980 Vol 50(2), pp. 278-285), bentonite (Carson, M. S. Thesis University of Guelph, Canada 1982) and spent bleaching clay from canola oil refining (Smith, Can. J. Animal Science. 1984, Vol. 64, pp. 725-732), have been shown to diminish the adverse effects of T-2 toxin and zearalenone in rats and immature swine. The adsorption of aflatoxin B1 from various liquid media by a variety of phyllosilicates, including montmorillonites, has been reported (Masimanco et al., Ann. de Nutrition et Alimentation, 1973 Vol. 3, pp. 137-147). A detailed study (Phillips, et al., Poultry Sci.. 1988, Vol. 67, pp. 243-247) using a range of minerals including montmorillonites has shown that various members of the series exhibit differing levels of activity in vivo and in vitro for the adsorption of aflatoxin. The calcium montmorillonite identified as Clay A in the accompanying table has been supplied commercially as a feed additive.
It had been observed that calcium montmorillonites (with high exchangeable divalent plus trivalent/monovalent cation ratios) were superior to sodium montmorillonites (with low divalent plus trivalent/monovalent cation ratios). It has been recognized that even calcium montmorillonites vary significantly in their ability to adsorb aflatoxins and that there is indeed an appreciable difference between chemically similar montmorillonie clays. However, no ready explanation was available to guide a determination as to which physical or chemical property was responsible. Among various calcium montmorillonite in situ binding capacity could not be correlated with any single physiochemical property.
Accordingly, it is the object of the instant invention to provide a means for selecting among the wide varieties of clays those montmorillonite clays which are most effective in adsorbing mycotoxins, especially aflatoxins.